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Speed Read

Chemical Exchange Scheme

Swapping goods and possessions can lead to unexpected surprises, and in the case of chemistry this is no exception. One of the most popular and useful reactions that chemists use to build new molecules involves a curious process in which particular atoms switch their molecular partners, and the 2005 Nobel Prize in Chemistry rewarded three researchers who pioneered our understanding of how this extraordinary event occurs.

The reaction in question, metathesis, performs a cut-and-paste act on two molecules that each contain a double bond between carbon atoms. For over a decade, chemists working in petroleum refining had observed this baffling rearrangement, in which both molecules are cut across their double bonds, pieces from one molecule are swapped with a piece from the other, and then these pieces are attached together to create new double bonds. Yves Chauvin was the first to propose the correct mechanism behind this reaction; a metal catalyst attaches itself to carbon atoms held together by a double bond and facilitates this cutting, switching and stitching process.

Chauvin's theory set the scene for chemists to hunt for and design catalysts that carry out the exchange scheme effectively. After examining a number of different candidate metals Richard Schrock made the initial breakthrough by discovering that catalysts containing the transition metal elements molybdenum and tungsten performed the task. However, their tendency to react unfavourably meant that the reaction did not always fully go to plan. Robert Grubbs went one stage further by developing more effective catalysts centred around another transition metal, ruthenium, which reacted less with other molecules and was much more stable.

With these more effective ruthenium catalysts, the use of this reaction in industry rocketed. Since molecules containing carbon, or organic molecules, are the lifeblood of industries as diverse as plastics and pharmaceuticals, chemists have used the metathesis reaction to create a host of important products. One huge advantage of metathesis in relation to many conventional reaction methods is that it produces chemicals in a much cleaner, cheaper, and more efficient manner. By switching to this reaction, chemists hope to develop environmentally friendly ways of building new organic molecules.

This Speed Read is supported by the Camille and Henry Dreyfus Foundation Special Grant Program in the Chemical Sciences.